Ensuring that reacting species achieve optimal physical contact can be among the most difficult challenges in chemical reactor design. If done improperly, numerous undesired byproducts and an abundance of unreacted reactants can seriously erode the economics of the system. The reactor type (i.e., batch, plug flow, stirred tank, or combinations thereof), reactant and product diffusion, pressure effects, and other factors must all be considered in selecting or fabricating a reactor system best suited for use in a given reaction.
Reactor residence time and reaction conditions such as pressure and temperature impact the percentage of atomic or molecular collisions and thus affect yield, throughput, and selectivity. Backmixing is another phenomenon which can contribute to further reaction of the reactor products. Backmixing is the mixing of a molecule or intermediate which has been present in the reactor for a given length of time with a molecule or intermediate which has been present in the reactor for a lesser period of time. The amount of backmixing that occurs can be related to reactor geometry and type; fluid dynamics of the reactants, intermediates and products produced in the reactor; and other factors. In some processes optimizing the production of products by adjusting these parameters is easily understood and straightforward.
The employment of finely tuned catalyst can complicate reactor design and reaction control. For example, U.S. Pat. No. 5,395,857 proposes that in the production of bisphenol A (BPA) in a downflow reactor, the degree of crosslinking of certain ion exchange resin catalysts directly affects the physical performance of the process as well as the reactivity and selectivity of the reaction. There the inventors found that the deleterious hydraulic impact attributable to catalyst particle shape and the compression of the catalyst bed due to pressure can be ameliorated by using a two layer catalyst in which at least one of the layers comprises a ion exchange resin catalyst which exhibits a 2% or lower degree of crosslinking. The process is directed to increasing the volume and time yield of fixed bed reactors. It would be further desirable to employ an ion exchange resin catalyst such as the one proposed in U.S. Pat. No. 5,395,857 because of the greater selectivity and activity offered by such catalysts and because resin based catalysts with greater degrees of crosslinking tend to desulphonate more readily.
It is sometimes desirable or necessary to conduct reactions in the upflow mode. For example, in downflow processes the potential for catalyst bed collapse at high flow rates because of the low degree of crosslinking and the effects that this has on the physical properties of the catalyst must be considered. Increased byproduct production attributable to longer residence times must be also be considered. Thus, it would be desirable to operate the reactor in the upflow mode to allow the resin bed to fluidize instead of collapsing and to take advantage of possible selectivity improvements.
We have also found that if one could effectively operate in the upflow mode it would be possible to employ reactors of much smaller size to achieve comparable throughput and selectivity improvement relative to those used in downflow reactors due to significant reduction or elimination of pressure drop through the reactor. Unfortunately, fluidization in the upflow process leads to back-mixing of the catalyst and reactor feed. This reduced plug flow characteristic reduces per pass conversion of reactants to products and can lead to wasteful catalyst entrainment known to be a problem with upflow reactors.
Chemical process technology could benefit generally if it were possible to improve catalyst and fluid behavior within reactor systems. More particularly, chemical processes conducted in upflow reactor systems could prove advantageous if the aforementioned problems were resolved.